Technical Abstract:
Porcine reproductive and respiratory syndrome virus (PRRSV) infection is a cause of respiratory disease in neonates and nursery pigs and/or reproductive losses in breeding animals. Coinfection of pigs with other bacteria may be one cause of the often hard to treat respiratory disease observed in nursery pigs. We coinfected pigs with Salmonella choleraesuis and PRRSV to determine if coinfection causes any change in disease outcome as related to salmonellosis. Pigs (34- or 35-days-old) were randomized into 5 treatment groups. Pigs in group 1 were uninoculated controls. Pigs in groups 2 through 4 received PRRSV on day 0 (10**4.5 TCID); S. choleraesuis on day 0 (10**4 or 10**8 CFU); S. choleraesuis on day 0 (10**8 CFU) and PRRS on day 3; and S. choleraesuis on day 0 (10**4 CFU) PRRSV on day 3 and dexamethasone (2 mg/kg) IM on days 3 through 7, respectively. PRRSV and S. choleraesuis was given by intranasal instillation. Clinical signs, temperature, body weight, and Salmonella shedding were monitored over time. Clinical signs were more severe in pigs that were coinfected with or without dexamethasone and temperatures were greatest in pigs that were coinfected as compared to all other groups. Body weight increase was highest in the controls and lowest in the coinfected pigs with or without dexamethasone. Shedding was highest and occurred for a longer period of time in coinfected pigs. Dexamethasone extended the shedding, especially in pigs receiving 10**4 CFU S. choleraesuis. These data indicate that coinfection of pigs with PRRSV and S. choleraesuis results in decreased performance and increased shedding of Salmonella when compared to controls or either pathogen alone. Additionally, use of dexamethasone as a stressor may exaggerate these differences.